1. Field of the Invention
The present invention relates to an abnormality detection device of a fuel pump for a water jet propulsion boat propelled by ejecting water drawn through a jet pump that is driven by an engine using a fuel which is pumped from a fuel tank by operation of the fuel pump.
2. Description of the Related Art
Some water jet propulsion boats are equipped with an apparatus detecting the abnormality occurred in a fuel system providing a fuel from a fuel tank to an engine (refer to JP-A-2002-161800, for example). This type of water jet propulsion unit has a fuel pressure sensor in a fuel piping connecting the fuel tank and the engine in order to detect the pressure of fuel running through the fuel piping. During the fuel pressure sensor detecting the pressure of the fuel running in the fuel piping, if the detected value becomes abnormal, it is determined that an abnormality has occurred in the fuel system, and then an action such as stopping the fuel pump operation is performed.
However, the conventional fuel pressure sensor described above for water jet propulsion boats is constituted by precision instruments typically including strain gauges and circuits for signal amplification or transformation, and is therefore structurally weak against vibrations. The fuel pressure sensor is often exposed to hard vibrations since the water jet propulsion boats are highly motile and plane in high speed on the wavy water surface. Therefore, the vibration forces on the water jet propulsion boat may cause an error to occur in the value detected by the fuel pressure sensor and also may damage the fuel pressure sensor.
In order to prevent such problems, an attachment of the fuel pressure sensor must be strongly built to protect the fuel pressure sensor from damage caused by the hard vibration. Also, the structure of the attachment must be designed to prevent the vibration from being transmitted to the fuel pressure sensor. The attachment needs to be removable so that the fuel pressure sensor can be exchanged easily in case of breakdown. For the above reasons, the use of the fuel pressure sensor as an abnormality detection device of the water jet propulsion unit leads to a high cost, an increase in the number of parts, an increase in man-hours required for the assembly process, limitation of layout and such. In addition to this, if the fuel pressure sensor were used as an abnormality detection device in a water jet propulsion boat and if the fuel pump sucked the air temporarily, which causes the decrease of the fuel pressure, the fuel pressure sensor may determine that the fuel pump operation is abnormal even if the fuel pump has been operating normally.